When you use Google search and other Google products, they collect
a tremendous amount of information and use that information to
customize and better serve the ads that are the core of their
business. Many users don’t even realize this is happening,
others are comfortable with it and have some level of trust for
Google’s intent in using that data.

Well, Apple doesn’t trust the benevolence of Google, developers,
and other third parties involved in the iOS platform. Apple
wants to control the flow of user information.

And:

The thing is, Apple is a hardware company, that’s where they
have and will continue to make their money. Google, Facebook, and
others trade in information. The more detailed and specific, the
more valuable that information. For Apple, the better the overall
experience of the device, the more valuable that device becomes.
They can throttle ad targeting and the specificity of 3rd party
analytics according to the taste of users. Trusting 3rd parties to
do so would be incredibly foolish, and Apple seems to have just
recently figured that out.